A disc screen typically includes a frame in which a plurality of rotatable shafts are mounted in parallel relationship. A plurality of discs is mounted on each shaft and a chain drive rotates the shafts in the same direction. The discs on one shaft interleave with the discs on each adjacent shaft to form screen openings between the peripheral edges of the discs. The size of the openings determines the dimension (and thus the type) of material that will fall through the screen. Rotation of the discs, which have an irregular outer contour, agitates the mixed recyclable materials to enhance classification. The rotating discs also propel the larger articles which are too big to fall between the discs across the screen. The general flow direction extends from an input area where the stream of material pours onto the disc screen to an output where the larger articles pour off of the disc screen. The smaller articles fall between the discs onto another disc screen or a conveyor, or into a collection bin.
The discs of a disc screen normally have a central opening or bore that permits the discs to be slid over an end of a shaft which may have a round or square cross-section. See for example U.S. Pat. No. 4,836,388 of Bielagus. Eventually, discs wear out and must be replaced. It is not practical to refurbish or repair damaged or worn discs without removing them from the shafts of the disc screen. However, it is tedious to dismount the ends of the shafts of a disc screen from their respective bearings so that the old discs may be removed and replaced by sliding the discs off the ends of the shafts. If only a single disc is worn or broken, it is usually necessary to remove several discs before the damaged or broken disc may be slid off the shaft for replacement.
Previous attempts have been made to develop spot discs as manufactured by CP Manufacturing, Inc. of National City, Calif. See U.S. Pat. No. 6,318,560 of Robert M. Davis. The split disc is comprised of two identical halves which are assembled around a shaft and tightly held together by a pair of bolt assemblies which clamp the disc to the shaft. Each disc half is made of an outer rubber portion which is stiffened with a rigid internal metal frame embedded inside the rubber portion. While the aforementioned patented two-piece disc construction has been commercially successful, it would be desirable to provide a disc construction that is even more convenient to remove and install while offering a lower part cost for replacement of worn or damaged discs in a disc screen.
Past inventions have attempted to provide useful discs comprising rigid, metal frames embedded within a flexible material, such as urethane, such that the rigid, metal frame extends substantially in a radial direction within the flexible material to provide stiffness to the disc. A disadvantage with these past inventions is that excessively rigid metal frames can be expensive and heavy. A load of discs may be shipped long distances at rated depending upon the freight weight. A load of discs laden with heavy, rigid, metal frames can be excessively costly to transport. A lighter disc would offer substantial savings when multiplied by the number of discs shipped at a lighter freight weight. Additionally, using less metal (or even no metal) may reduce material costs, machining time, other factors to provide an improved disc.
Thus it would be advantageous to use a disc that minimizes manufacturing costs, comfortably operates, saves freight costs, reduces weight of the device, and provides stability in rotation, and offers a flexible outer surface, optionally with a tongue-and-groove feature, particular clamping features, and other beneficial features.